CA1176700A - Electrochemical cell and an anode structure for an electrochemical cell - Google Patents
Electrochemical cell and an anode structure for an electrochemical cellInfo
- Publication number
- CA1176700A CA1176700A CA000387044A CA387044A CA1176700A CA 1176700 A CA1176700 A CA 1176700A CA 000387044 A CA000387044 A CA 000387044A CA 387044 A CA387044 A CA 387044A CA 1176700 A CA1176700 A CA 1176700A
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- Prior art keywords
- carrier
- cell
- electrolyte
- substance
- electropositive
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
- H01M4/664—Ceramic materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/36—Accumulators not provided for in groups H01M10/05-H01M10/34
- H01M10/39—Accumulators not provided for in groups H01M10/05-H01M10/34 working at high temperature
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/64—Carriers or collectors
- H01M4/66—Selection of materials
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/409—Separators, membranes or diaphragms characterised by the material
- H01M50/431—Inorganic material
- H01M50/434—Ceramics
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M50/00—Constructional details or processes of manufacture of the non-active parts of electrochemical cells other than fuel cells, e.g. hybrid cells
- H01M50/40—Separators; Membranes; Diaphragms; Spacing elements inside cells
- H01M50/489—Separators, membranes, diaphragms or spacing elements inside the cells, characterised by their physical properties, e.g. swelling degree, hydrophilicity or shut down properties
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M2300/00—Electrolytes
- H01M2300/0017—Non-aqueous electrolytes
- H01M2300/0048—Molten electrolytes used at high temperature
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P70/00—Climate change mitigation technologies in the production process for final industrial or consumer products
- Y02P70/50—Manufacturing or production processes characterised by the final manufactured product
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- General Chemical & Material Sciences (AREA)
- Ceramic Engineering (AREA)
- Materials Engineering (AREA)
- Inorganic Chemistry (AREA)
- Manufacturing & Machinery (AREA)
- Secondary Cells (AREA)
- Battery Electrode And Active Subsutance (AREA)
Abstract
ABSTRACT
The invention provides an electrochemical cell and an anode structure for an electrochemical cell. The anode structure comprises a substantially non-electronically conductive micromolecular sieve carrier wherein electro-chemically active anode material in the form of an electronically conductive electropositive substance is sorbed and held in dispersed form, and a reservoir or source of the electropositive substance in contact with the carrier. The electropositive substance is liquid at the operating temperature of the cell.
The invention provides an electrochemical cell and an anode structure for an electrochemical cell. The anode structure comprises a substantially non-electronically conductive micromolecular sieve carrier wherein electro-chemically active anode material in the form of an electronically conductive electropositive substance is sorbed and held in dispersed form, and a reservoir or source of the electropositive substance in contact with the carrier. The electropositive substance is liquid at the operating temperature of the cell.
Description
670~
THIS INVENTION relates to an electrochemical cell, and to an anode structure for an elec-trochemical cell, suîtable for secondary use (rechargeable~.
In recent times, increasing atten-tion has been given to the development of energy storage mechanisms.
These developments have, however, been retarded to varying degrees hy the difficulties involved in effectively controlling mobile electrochemically active substances, and by the difficulties involved in operating at the elevated temperatures which in many cases are necessary for the effective operation of electrochemical cells.
~ ccording to one aspect of the invention, khere is provided an electrochemical cell which comprises an anode which includes as its electrochemically active anode material an electronically conductive electropositive substance which is molten at the operating temperature of the cell, a compatible electrolyte; and a compatible cathode, the cell further comprising a substantially non-electronically conductive micromolecular sieve carrier wherein the electro positive substance is sorbed and is held in dispersed form, the micromolecular sieve carrier being liquid-tight and located between and separating the electrolyte and cathode from the electropositive substance of the anode.
By liquid-tight is meant that all of the electro-chemically active species, when going from the anode to the ' 6~
: -3-cathode or vlce versa, has to go via the internal ore (cavity structure of the carrier~.
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, According to another aspect of the invention, there is provided a composite anode structure cornprising a subs~anti.ally non~electronically conductive ~icro-molecular sieve carrier wherein electrochemically active anode :. material in the form of an electronicall~ conductive electro-positive substance is sorbed and held in dispersed form; and a reservoir or source of the electropositive substance in contact with the carrier, for use with a compatible electrolyte and cathode in an electrochemical cell wherein the electropositive substance of the reservoir is molten and is separated by the carrier from the electrolyte.
` Without being bound by theory, the Applicant believes that .~ the electropositive substance may form electronically conductive .~ pathways extending along at least some of the channels and/or pores in the carrier, thereby placing at least so~e of the windows in the surface of the carrier in electronic contact with one another via the interior of the carrier. These path-~ ways, in use, can thus act to render the carrier, when it i5 r doped with the electropositive substance, electronically . conductive as a whole, via the pathways, so that electrons can be conducted along the pathways from the interface between the . carrier and the electrolyte, to the interface between the carrier and the el.ectropositive substance of the anode~
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` , --'1--The Applicant believes that it may be possible that the electropositive substance is sorbed in elemental form, the electropositive sub`stance being held in dispersed form in the carrier, and being mobile in atomic or elemental form along the channels and/or pores of the carrier to occupy suitable sites which have beèn vacated by other atoms of the electro-positive substance, so that it can move, in use, through the carrier from -the anode to the electrolyte.
When there is a danger, as when the electrolyte is liquid at the operating temperature of the cell, that the electro-positive substance may react chemically in an undesirable fashion with the electrolyte, e.g. with anions of the electrolyte, the carrier, when it contains the sorbecl electro-positive substance, may be selected or modified such that the windows in its surface to its microporous interior, prevent sufficient access to the interior of the carrier of e.g. the anions of the electrolyte, for the undesirable reaction to take place. Likewise, when as described hereunder the electrolyte selected is an aqueous solution, the carrier, when containing the sorbed electropositive substance, may be selected or modified such that the windows or pores in its surface do not permit access to its interior of water molecules.
The electropositive substance will be molten at the operating temperature of the cell and may comprise or include an alkali metal or alkaline earth metal, a combination or alloy of two or more alkali metals or alkaline earth metals, or a combination or alloy of one or more alkali metals or alkaline earth metals with one or more other substances. In other ~;
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words, the alkali metal or alkaline earth metal or metals may be used alone or in combination of -two or more thereof, or one, two or more thereof may be used in a composition or alloy with one or more compatible other substances, provided they are such that the electropositive substance is molten at the operating temperature of the cell.
~ he al~ali metal or metals of the electro-positive substance may be in any suitable combination containing for example lithium, sodium, and/or potassium. The alkaline earth metals may likewise be in any suitable combination of alkaline earth metals, such as calcium or magnesium. The electro-positive substance, as mentioned above, is molten at the operation temperature of the cell. For use at atmospheric pressure, certain alloys of sodium and potassium are particu-larly suitable as they have melting points below 100C, and potassium and particularly sodium can be considered for use alone because of their availability at competitive prices.
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By 'micromolecular sieve carrier' is meant a molecular sieve carrier having interconnected cavities and/or channels in its interior and windows and/or pores in its surface leading to said cavities and channels, the windows, pores, cavities and/or channels having a size of not more than 50 Angstroms and preferably less than 20 Angstroms, or, when for use with an electrolyte which is an aqueous solution, such that water molecules cannot be sorbed into the interior of the carrier, irrespective of whether other sorbed species are present in the cavities of the carrier.
~ .1767~
Suitable micromolecular sieves are minexal micromolecular sieve carriers, i.e; inorganic lattice or framework structures, although certain essentially organic micromolecular sieve carriers such as clathrates may, in certain circumstances, be suitable as mentioned hereunder.
Suitable mineral micromolecular sieve carriers may be selected from tha group of substances which make up the ; tectosilicates, i.e. the class of substances also known as "framework silicates" which may be natural or synthetic, crystalline or non-crystalline/amorphous, and which include:
silicates, e.g. silica gel zeolites felspars felspathoids being silicates of a structural type in which all four oxygen atoms of the silicate tetrahedra are shared with neighbouring tetrahedra. rrhe framework of the tectosilicate is made up of silicon atoms ~ith in some cases aluminium atoms, together with other atoms. Mineral micromolecular sieves include also mixtures of or analogues of tectosilicates in which the silicon and/or aluminium atoms of the framework may be substituted amongst others by atoms of one or more of:
lron beryllium boron phosphorous carbon germanium and gallium .
,;
~ 17~0~
in minor or major proportions and wherein the micromolecular sieving characteristics and properties are unaffected by the substitution. As long as their properties relevant to the present invention are substantially unaffected, these analogues are regarded as tectosilicates in the context of the present specification.
Conveniently, for molten salt electrolytes, the micro-molecular sieve carrier is a zeolite, or when the electrolyte is to be a~ueous, the carrier may he a tectosilicate which cannot sorb water e.g. a felspar or ~elspathoid.
- Zeolites, felspars and felspathoids are in a class of crystalline or amorphous natural or synthetic materials which contain aluminium and silicon in fairly definite proportions, . .~
and their analoyues. For a more detailed discussion of zeolites, reference can be made to the January 1~75 publication of the International Union of Pure and Applied Chemistry entitled 'Chemical Nomenclature and Formulation of Compositions, of Synthetic and Natural Zeolites'.
Zeolites contain sorbed water molecules which may be removed, usually reversibly, by heat and/or evacuation. While it is e~pected that zeolite molecular sieye carriers which are at least partially dehydrated and usually ~ully dehydrated will generally be used, the presence of water in the zeolite may, in certain cases, be an advantage to enhance ionic conductivity depending on the mechanism of the cell reaction as discussed hereunder.
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Zeolites felspars and felspathoids are usually possessed of a reasonably ord~ered internal structure, exhibit a high internal surface area and are characterised by the presence of a multiplicity of regular arrays of molecular cayities, i.e.
channels and/or cavities opening out of the surface of the ~eolite via windows and/or pores. Other tec-tosilicates, particularly if amorphous or non-crystalline, have a substan-tially less ordered or indeed unordered internal structure, while however retaining suitable arrays of molecular cavities.
It is believed that zeolites i.n their hydrated form can be represented by the following structural formula:
M2~nO-A1203-xsiO2-yH2 where M is a cation of n valance; and X and Y are independent variables that are a function of the composition of the starting mixture, and the manner of formation.
It has been found that suitable tectosilicate crystals can have a sufficiently high physical strength for effective use in the cell of the invention. ~When the tectosilicate is a powder, it may be compacted and supported, for example in a porous container for use).
In addition, it has been found that tectosilicate crystals which have been doped with an electropositive substance can be sufficiently resistant to electrochemical and thermal damage during repeated use in a cell according to the present invention.
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When crystalline tectosilicates are used, physical or electrochemical failure of tectosilicates doped with the electropositive substances should thus not be factors which contribute significantly, if at all, towards failure of cells according to this invention.
In the present invention the micromolecular sieve carrier is de~igned to havè a three-dimensional structural skeleton which remains physically and electrochemically stable, so that it will not collapse significantly as a result of the electro-chemical reaction during normal use, and will continue to function as a sieve permitting diffusion therethrou~h of the electropositive substance, while prevent.ing access to the electropositive substance in its interior by anions of the electrolyte with which it is used, in cases where the anions react undesirably with the electropositive substance of the anode, and preventing access to water when the electrolyte is an aqueous solution.
These aspects should thus be borne in mind in selecting the particular molecular sieve carrier for use with the selected electropositive substances and electrolytes in carrying out the invention.
It should be noted, however, that when certain carriers are doped with extremely electr.opositive substances such as lithium metal alone or in combination with other metals, substantial modification of the carrier lattice can result. It has been found, h~wever, that such modified lattices still ' ' .
~ ~670~
possess the necessary properties in that they can act as carriers andjor sieves for the electropositive substance, are sufficiently electrochemically inert or relati.vely electro-chemically inert during use in a cell, and can preven-t access to the electropositive substance by undesireable chemical species or, when presen-t, water from the electrolyte.
Such carriers, for example tectosilicates such as zeolites which have been physi~ally and/or chemically modified during doping with the selected electropositive substances/ but which still possess the necessary properties, may thus be usefully employed as micromolecular sieve carriers in the anodes o~ this invention, and for the purpose of this specification, these modified tectosilicates, zeolites, etc., are still regarded as tectosilicates, zeolites, etc.
It should further be noted that in the case of some tectosilicates incidental cation exchange may occur during use of the anodes in ac~ordance with the invention, in some electrochemical cells. Such reactions are well known and merely change the sizes of the windows and pores of the carrier lattice, and this aspect should be borne in mind in selecting ~;
:~ the electropositive substance and carrier, to ensure that the ;. pores or windows of the carri~r are of a desired size to permit passage of the electropositive substance therethrough, while excluding water of the electrolyte when an aqueous electrolyte . is used in the cells, and undesireable anions of the electrolyte in cases where these anions are chemically unstable with ;
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respect to the electropositive substance. Once again,these are still regarded as -tectosilicates of the type in question.
Thus, it should be appreciated that while the tectosilicate molecular sieve carriers of this invention may, in certain instances, after doping or after having been subjected to several charge/discharge cycles in a cell, no longer strictly be in the form of tectosllicates as such in the usual sense, they may still be regarded as such, or at least as mineral micromolecular sieve carriers in the context of this invention, provided they exhibit the requisite properties.
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Thus, where the tectosilicate molecular sieve carriers of the eleetrodes of this invention are in the form of modified tectosilieates, they are such that while physieally or ehemically modified, they still possess the appropriate molecular cavities or pores for receiving the electropositive substance, still possess the channels or pores which lead to the cavi~ies, and still have windows of the appropriate size.
Thus, where the moleeular sieve carriers of this invention are in the form of modified substances, they will be those which have windows, channels, pores and cavities for receiving the electropositive substances, and for permitting passage therethrough of the electropositive substances, while excluding water and/or undesireable electrolyte anions.
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By taking into consideration factors such as pore or channel size, cavity size and window si~e, and the ability to sorb electropositive substances in effective ~uantities, while permitting high mobility or passage therethrough of the electropositive substances and while excluding water and/or such anions of the electrolyte which are unstable with respect to the electropositive substances therefrom, a rough guide can be obtained for the selection of the appropriate micromolecular sieve carriers for use in accordance with the inven-tion.
Further factors which can serve as a guide, can be the degree of porosity, the density, the availability, and the mechanical strength, the stability and the electronic conductivity or absence thereof, of the doped micromolecular sieve carriers.
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For example, sodalite has the right structural properties to permit it to function as deseribed herein as a micromolecular sieve carrier for the purpose of this invention. Such alumino-silieates, or the like, which exhibit acceptable structural properties to function as required by this invention, may be suitable tectosilicate molecular sieve carriers~
The micromolecular sieve earrier should preferably thus be such -that the electroposi-tive substance when sorbed therein, will be held therein in finely dispersed elemental form, e.g.
possibly in atomic, mole.cular, atomic cluster or molecular cluster form to present its greatest availability for electrochemical activity during use.
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The carrier should further preferably be such that it will hold an effective amount of the electropositive substance therein for effective electronic, and if necessary ionic, conduction for the electropositive substance to move there-through in effective quantities.
In the present invention, it is believed -that the carriers may in fact act as sieves, permitting dif~usion therethrough of the electropositive substances in elemental, atomic or ionic form from the anode to the electrolyte during discharge of the cell, while preventing access to the electropositive substances contained therein hy water and/or the anions of the electrolyte if unstable with respect to the electropositive substances. In use, the function of the carriers is thus to prevent reduction of the electrolyte by the electropositive substances contained in the anode, and to prevent reaction of these electropositive substances with any water in the electrolyte. It is contem-plated that the cell of the present invention can, if desired, be used as a secondary or rechargeable cell, and during charging, the electropositive substances will diffuse from the electrolyte to the anode.
The anode structures of the present invention are of particular utility in electrochemical cells employing liquid molten salt electrolytes or aqueous solution electrol~tes and designed to operate at relatively low temperatures, for example, of the order of room temperature up to about 360C.
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In such cells, the cathodes can comprise an oxide of one or more transition -m~etals selected for example ~rom the group consisting of ma~ganese, iron and nickel~ or an intermediate refractory hard metal compound of at least one metal selected from the group consisting of chromium, manganese/ iron, cobalt and niakel, with at least one non-metal selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorous which has been activated by halogenation. Thus, for example, the cathode may comprise a refractory hard metal compound which is an activated carbide, of iron~ chromium or manganese.
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Instead, the cathode may comprise sulphur and/or selenium, and a micromoleaular sieve carrier, for example a tectosilicate, '~! wherein the sulphur and/or selenium is sorbed, and is held captive during use of the cathode in the cell. The sulphur and/or selenium may for example be sorbed into a dehydrated ; zeolite molecular sieve carrier which may be selected from the group consisting of erionite, faujasite, synthetic zeolite 3A, zeolite 4A, and zeolite 13X. The zeolite carrier material will be made electron conductive by addition of a suitable electron ` conductive material such as graphite.
: .
:, For such low temperature cells, the electrolyte may be an aqueous acid or base, for example an aqueous solution of sodium hydroxide or potassium hydroxide, or it may be a molten inorganic salt such as an iodide-based inorganic salt electrolyte.
Thus, to test this possibility, the eutectic mixture of lithium iodide/po-tassium iodide was prepared in the ratio described by "
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; D B Leiser and A J ~hittemore Jr. ~ ~mer. Ceram' _oc. 50 (19611, 60. This mixture was doped with ~9,5~ pure strontium iodide o~tained from Cerac Inc. The components were mixed and qround toget~er into a Eine powder and melted in glass tubes under à flowing stream of argon gas.
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The -temperatures were recorded where -the mixtures 1 melted and solidified. The homogeneous solid mixtures were subsequently ground and accurate melting point determinations were carried out. The strontium iodide added varied ~etween about 25~ and a~out 5Q~ ~y mass of the mixture. Melting points were found to lie in the region of 220C and 240C, ,.
whereas the lithium iodide/potassium iodide eutectic mixture was confirmed to melt at about 260C.
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Instead the electrolyte may ~e a molten inorganic salt electrolyte ha~ing the general formula:
i M ~l Hal4 in which M comprises one or more alkali or alkaline earth metal cations and Hal comprises one or more halides, the proportions ,~ of the alkali or alkaline earth metal cations and halide anions ' conveniently being such that the above s-toichiometric product , ,':
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is maintained, and the alkali metal cations and halide anions being selected such that the electrolyte has a sufficiently low melting point to permit use in its molten state at the desired operating temperature of the cell.
When such electrolyte is used with a tectosilicate-based :~ carrier, and the electropositive substance of the anode, (for ~ example one or more alkali metals) is capable of reducing the .~; aluminium of the electrolyte to cause :it to plate out on the anode and/or separate from the electrolyte for example to .. precipitate, the window or pore size of the molecular sieve :
carrier of tha anode should be such that the windows exclude the Al Hal41 anions of the electrolyte Erom access to the interior of the zeolite of the anode. When these halide ions are AlC141 , the window or pore size o~ the tectosilicate should be such as comfortably to exclude these anions, whereas easily to permit access via the windows or pores to the interior of the zeolite of the electropositive material, for example atoms or ions of lithium, sodium and/or potassium.
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. In this way, the Al Hal41 anions are prevented from :- coming inta direct contact with the electropositive material in : its elemental or atomic/molecular form, so that reduction and separation of the aluminium by means of a back reaction cannot ,,,. ,:
directly and easily take placeO
.... .
Tectosilicate molecular sieve carriers which are suitable :
~ for use in conjunction with mol-ten salt electrolites of the , !,. .
;~. formula M Al Hal4, may be selected from the group consisting in :, .' ' ' .
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sodalitel carnegieite, zeolite 4A, zeolite 13X and mordenite.
In the case of aqueous electrolytes, testing them as the electrolytes in cells according to the invention having sodium/potassium anodes and cathodes comprisin~ manganese dioxide promises to provide excellent electrochemical ~ehaviour at operating temperatures below 100C.
, When such electrolytes are used with a tectosilicate-~ased carrier, the electropositive su~stance of the anode, (for example one or more alkali metals~ is capable of reacting with the water of the electrolyte, so the window or pore size of the molecular sieve carrier should be such that the windows exclude the water of the electrolyte from access to the interior of the anode. The windo~ or pore size of the tectosilicate should be such as comfortably to exclude water, whereas easily to permit access via the windows or pores to the interior of the anode of the electropositive material, for example atoms or ions of sodium, lithium, and/or potassium.
In this way, ~ater is prevented from coming into direct contact with the electropositive material in its elemental or atomic/molecular form, so that the undesired reaction cannot take place.
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: ,.;;, 1~ " ., ~ ~ithout being bound hy theory, it is ~elieved that in micromolecular sieve carriers which have cavities in the form ,.: .
i of capillary- or pipe-like channels, which may have a , ~
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approximately e~ual to the pore or windo~ ~ize, the electro-positive substan:ce can possibl~ move alony th.e channels during discharge from th.e source o~ electropositive material ~ to the in-terface ~etween the carrXer and the electrolyte, ;l and that in certain instances the electroposi-tive suhstance in the channels may maintain electronic contact with the . elec-troposi.tive substance reservoir throughout the body of the carrier. In oth.er words, the carrier will, in this ~ case, be electronically conductive, via the electropositive :: substance in the channels, between th.e reservoir or source of electroposi.tive substance and the electrolyte. In this : regard it will be appreciated that the source of electropositive : .
^- substance will not ~e in direct contact with the electrolyte, except via the doped micromolecular sieve carrier.
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. ~ In the case where the doped molecular sieve carrier is an electron conductor, one possible mechanism is that during :~ ~ discharge of the cell, atoms of the electropositive substance ~ ionize at the interface between the electrolyte and the }-,;'`.~
molecular sieve carrier, and the ions pass into the electrolyte, .. the eleotrons from said ionizat.ion passing via the electro-j~ positive su~stance in the interior of the carrier to said : source of electropositive material, which will act as or can be ,: ~ .....
associated with a current collector. At the same time, atoms of the electropositive substance will pass from said source of anode material into the molecular sieve carrier material to replace those which have been ionized, rapid diffusion of the :, ~ ., .
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electroposi-t~ive material taking place via the channels of the molecular sieve carrier from the anode towards the electrolyte.
According to this mechanism, the electropositive substance may be present in the form of electronically conductive threads or chains in the channels. It is possible, however~ that, instead of the electropositive substance being present in the Eorm of electronically conductive chains or threads in the channels, the elec~rochemically active sorbed electronically conductive substance atoms may form clusters with suitable cations forming part of the lattice or matrix o~ the molecular sieve material. These clusters may thus share electrons from the sorbed electropositive substance. Such electrons may be sufficiently mobile to move through the molecular sieve carrier from its interface with the electrolyte where ionization takes place, to the anode reservoir and thence to the collector.
... .
If the mechanism suggested above whereby ionization takes place at the interface between the molecular sieve carrier and . ~
the electrolyte is, however, incorrect and ionization takes place at the interface of the molecular sieve carrier and the anode or source of electro-positive substance, or a hybrid mechanism exists whereby ionization at the source is sufficient-ly predominant, then the molecular sieve carrier with the electropositive substance sorbed therein may not, strictly speaking, function as a sieve, but may instead function as a solid electrolyte. Ions instead of atoms will then diffuse rapidly through the molecular sieve carrier. This process may be enhanced by the presence of sorbed atoms in the form of 67~ ~
clusters, the solid electrolyte being metal rich, e.g. Na43+
clusters in sodali~e. However, whe-ther or not the carrier impregnated with the electropositive substance is regarded as a sieve or solid electrolyte, this does not affect its utility and function as described above, in the cells and anode structures of the present invention.
:
To prepare a carrie~ according to the invention~ a tectosilicate, for example a suitable felspar or felspathoid or .- .
~ a zeolite w~ich is fully or partially dehydrated by subjecting ,.~
it to vacuum and heat, is exposed, optionally under pressure and after having been subjected to a vacuum, -to a vapour of the electropositive substance to be sorbed into it. While it may ,~ not be necessary to saturate all the vacant sites in the ~ zeolite molecular sieve carrier with the electropositive ~....;
1 ; substance, and only a desired proportion o~ the vacant sites l` ' need be o~cupied thereby, in practice it is contemplated that as much of the electropositive material as possible will be sorbed into the zeolite molecular sieve carrier.
Pore or window size of the zeolite molecular sieve carrier may or may not, as the case may be, be modified by the sorption of the electropositive material, and the zeolite molecular sieve carrier will be chosen 50 that its channel and pore sizes, in particular its window sizes are, after doping, such ,,i, ; tha-t it operates effectively to exclude any anion which is unstable with respec~ to the alkali metal of the anode, or any ~ water from the electrolyte from reacting with the electro-:, ..
.:
:`:
`: : ` :
7~
positive substance in the channels in use. In other words i~
such modification takes place, the micro molecular sieve carrier and metals may be chosen so tha-t the molecular sieve carrier finally obtained has suitable channel, pore and window sizes.
Thus, lithium, sodium or potassium may be used alone or such alkali metals may be used together, or they may be used together with other metals such as, for example, aluminium. It is believed that when an electropositive substance such as sodium or lithium is used together with another metal such as aluminium, both the alkali metal and the other metal such as aluminium, may be sorbed in the carrier, the other metal modifying the zeolite molecular sieve carrier by reducing effective channel, pore and/or window sizes to a desired value appropriate for the intended use of the anode. Thus, starting with a molecular sieve carrier which has channels, pores and particularly windows which are too large to exclude undesire-able electrolyte ions, after sorption of the other metal these channels, pores and/or windows may be reduced in size by the presence of atoms of the other metal occluding them, so that they are at the right size to exclude any water or undesireable electrolyte ions, while permitting passage or entry of the electropositive alkali metal atoms/ions such as sodium, potassium and/or lithium.
.
The possibility is also contemplated that when the pore size of the carrier is sufficiently large, molecules of the electrolyte may, in the initial stage o~ the operation of the cell, be able to penetrate some way into the body of the carrier, .
' ' `' 7 0 ~
at which point a reaction will occur with the electropositive substance, the res~ultant products of which serve to reduce the cavity size, thereby preventing further penetration of the electrolyte and any further reaction, so that the action of the cell is as described above, e.g. when sodium is the electro-positive material, sodium aluminium chloride i5 -the li~uid electrolyte, and the reaction causes precipitation of aluminium metal which serves to block the cavities to the desired extent.
, .: It will thus be appreciated that ~ither a suitable molecular sieve carrier can be selected which initially has .... .
windows, pores and channels of the correct size, or one having ~ such sizes which are too large, can be selected and modified .s during the sorption process so that lt ends up with the pores, . channels and windows of the appropriate size. In this case, ~ . -s ::' the other metal, such as aluminium, or even nickel, which is .~ used together with the electrochemically active electropositive :;~
alkali metal, can form an effective lining to the channels, to remain there while being relatively electrochemically inert in the cell, acting to reduce the channel, pore and/or window sizes, and acting also to increase electronic conductivity along the pathways provided by the channels containing the electro-chemically active electropositive substance. Thus, certain species of the sorbed material can act to modify the molecular sieve carrier and to stabilize it while increasing its electronic conductivity along the pathways provided by the channels, whereas other species can act as -the electroposi-tive material. The electron-conducting properties of the molecular sieve carrier can thus, it is believed, be confined to the 7 ~ ~
channels, whereas the body of the molecular sieye carrier material or at least that part thereof which is in direct contact with the liquid electrolyte, will be non~, or neylig.i~
bly, electronicall~ conductive to prevent plating of cations from the electrol~te onto the surface of the anode exposed to the electrolyte during charging.
This feature acts to prevent dendrite formation which is in many instances a cause of cell failure, since the plating of the electropositive material can only take place inside the cavity structure of the carrier, thereby preventing it from becoming detached from the anode structure and/or causing internal short circuits.
;~
In specific embodiments of the invention when the carrier ' ~ is a zeolite, the anode can comprise sodalite with sodium sorbed therein; mordenite with suitable proportions of potassium and sodium sorbed therein; or mordenite with ~ .
suitable pr.oportions of potassium and lithium sorbed therein.
In a further specific embodiment of the invention, where the material of the molecular sieve carrier is a non-, or negligibl~, electronically conductive zeolite, it may be possible to dispense with a separate liquid electroly-te and to have the zeolite molecular sieve carrier in direct and in-timate contact with a suitable compatible cathode, such as sulphur sorbed into graphite-coated zeolite 4A. In this case, the :
sulphur (in the form of polysulphide) can act as the electrolyte and the zeolite with sulphur sorbed therein can be regarded as , . . .
~ 4-a catholyte. In this instance, thus, the zeolite/sulphur catholyte is regarded as a combined electrolyte/cathode and the , ., cells of the invention contemplate this possibility, with references to electrolyte and cathode in the context to be ~ construed accordingly. If the zeolite material of the anode is ;~ too electronically conductive to permit this, it may, however, . . ~, } be necessary to provide a porous insulating layer between the carrier and the cathode, impregnated with a suitable liquid electrolyte. This porous insulating layer may be a suitable insulating undoped dehydrated zeolite material. This embodi-;~ ment has the advantage that, apart from the anode or source of ,~i::
electropositive material, which will generally be molten, the cell will be substantially solid and zeolite-based.
, ,~ .
.;
It is further contemplated, when the cell can operate at a sufficiently low temperature, clathrate micromolecular - sieve carriers can be used in the same way as the previously , ., . mentioned mineral micromolecular sieve carriers. They should - not, when used with aqueous electrolytes, for the same reasons, ~: .
~- be capable of sorbing water, and should have a similar channel-` type structure, and similarly non-tectosilicate oxide micro-` molecular sieve carriers may be used.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows a schematic diagram of a device used as a conductivity cell for conductivity tests carried out on a zeolite carrier for a cell according to the invention;
. '' .
' ,. : , .
o ~ ~
Figure 2 shows a similar diagram o~ a test cell according to the invention; and Figures 3 and 4 show graphical results of tests conducted with the device of Figure 1.
. ' ~
In Figures 1 and 2 of the drawings, the same ; reference numerals are used for the same parts, unless ,~
otherwise specified.
In Figure 1, a conductivity cell generally designated 10, comprises a pair of stainless steel cups 12 held together by peripherally spaced insulated locking screws 14. In the cups 12 are molten alkali metal electrodes 16, and they are separated by a carrier 18 for a cell according -to the invention.
The carrier is clamped between the rims 12.1 of the cups 12 and acts to separate the electrodes 16 from one another.
In Figure 2, essentially the same arrangement is shown, except that one of the electrodes 16 is replaced by a liquid electrolyte/cathode mixture 20, so that the electrode 16 iS an anode and the cups 12 act as current collectors.
'''.
The invention will further be described, with reference to the following non-limiting examples, carried out with the device and the cell of Figures 1 and 2.
:;' ~) . :
:
. ~
; EXAMPLE 1 With reference to Figure 1, the carrier 18 was made in the form of a compact or pellet containing zeolite 4A and kaolin. A
mixture of equal parts by mass of zeolite 4A and kaolin was ball~milled for 24 hours, and a pellet was pressed on a linear ;~ press at a pressure of 2x105 kPa. The pellet was fired at 650C for 3 hours. After cooling, the artifact was placed in a ~` ~ freshly prepared zeolite 4A gel in which the kaolin was converted to zeolite 4A and the pel:Let was further densified by ~ 1 .'" .
~c~ back impregnation of the zeolite 4A from the fresh gel.
' ~' `
- The fully densified pellet artifact was removed from the ge:L
,~1~,~
i after 10 days, washed with distilled water and dehydrated at ``;~ 360C and 10 kPa for 6 hours. The pellet was then subjected to : sodium me-tal impregnation from the gas phase under a vacuum at 350C for 2-3 hours.
! .:
The pellet loaded with sodium sorbed therein was then handled ~ in a glovebox containing dry argon, and the device of Figure 1 `~I was constructed, and electrically connected to form a conduc-tivity cell. This procedure was repeated a number of times, and a number of such conductivity cells were constructed, employing also potassium and lithium as dopants.
Alternatlng current (AC) resistance R, against temperature T, was measured for the pellets. A typical graph of pellet conductivity as log 0' T (wherein ~ is the specific conductivity defined as = A R where d is pellet thickness, A is pellet ':
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:~ -27-cross-sectio~nal area, and R is the measured resistance in ohms) against temperature ( T 1 is shown in Figure 3.
. .
Comparative summarised test results are set out in the - following Table, Table 1 which compares a sodium impregnated :~ pellet with pellets impregnated with lithium and potassium respectively:
; TABLE 1 , Metal (5~cm) 1 TC
. Li 0,006 350 . Na 0,050 350 ~: K 0,010 350 :
Further compacts or pellets were made containing zeolite 4A.
..''`' The pellets of Example 2 were then dehydrated and treated with sodium, as described in Example 1 and tested at different temperatures.
.
~ Figure 4 shows a typical plot of log~T against 10 using the conductivity cell of Figure 1.
Test resul-ts are summarized in -the following Table, Table 2, ror sodlum:
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~, '` ` (-Lcm) 1 TC
~`:"; 0,006 20Q
0,020 250 ~.
~`. 0,060 300 ., .
~ ..
~^;. EXAMPLE 3 ~.
Small electrochemical test cells were made in accordance with Figure 2, comprising an alkali metal anode 16, a zeolite having the alkali metal sorbed therein as the pellet 18, and a suitable compatible liquid electrolyte and cathode 20. A test was conducted using a sodium anode, a zeolite 4A impregnated with sodium as the pellet, and a potassium iodide/ lithium iodide molten salt electrolyte mixed with cathode materi.al comprising zeolite 13X crystals doped with sorbed sulphur and containing graphite for electronic conductivity. In this case, an open cuxrent voltage of 1,9V was obtained together with a short circuit current of 35 mA, with an effective surface area of about 1 cm2 at 300C.
A further cell was constructed using potassium for the anode, a zeolite 4A for a pellet impregnated with potassium, a lithium aluminium chloride electrolyte and a zeolite 4A containing impregnated sulphur as the cathode.
In this case, an open current voltage of 2,0V was obtained, with a short circuit current of 5 mA at a temperature of 200C, with an effective surface area of about 1 cm2.
; ,"1 '`'' '','.
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. . .
-29~ 70~
. -:; Finally, a cell was constructed using a sodium anode, sodium ; impregnated into a zeoli-te carrier, a sodium aluminium chloride -~ electrolyte, and as a cathode sulphur sorbed into zeolite 4~.
From this cell an open current voltage of 1,9V was obtained, with a short circuit current of about 10 mA, at 200C with an :~ effective surface area of about 1 cm2.
. ~ .
.~, In all the above cells, the zeolite of the carrier was prepared by mixing with kaolin as described in Example 1.
' .1 .
~, .
All the cells described above failed at various times, for reasons essentially unrelated to the electrochemistry thereof, such as sealing problems, artifact cracking, etc. I-t is expec-ted that routine experimentation will overcome these problems. While some of these cells failed after a matter of .:
~ `, hours, others lasted up to 7 days.
: ~ ;
` An advantage of the present inven~ion is that it provides a cell in which the electrolyte is separated from the anode by a carrier which has a conductivity several orders of magnitude I higher than that of undoped tectosilicates, e.g. the zeolites reported in Breck, Donald W. 'Zeolite ~olecular Sieves', published by John Wiley & Sons, 1974, at pages 397 to 410.
, ~
It should be noted that the carrier tested, as appears ~rom Figures 3 and 4 hereof, has a conductivity which increases with the operating temperature i.e. it shows a positive temperature coefficient of conductivity which indicates that the conductivity may be ionic or hybrid rather than purely metallic or electronic.
..
' 7 ~ ~
. .
..
As regards the construction of the carrier of the present invention, it is intended to be completely liquid-tight in use.
For this reason ever~ attempt should be made to make it completely dense, with no macroporous spaces, channels, etc., therein. As regards its function, it should further be noted that, after such initial stabilization or conditioning period as may be necessary, there is in fact no change in the average chemical composition of the carrier during charging and :
discharging, and no change in the average oxidation state of the electropositive substance therein.
,'`, :.
THIS INVENTION relates to an electrochemical cell, and to an anode structure for an elec-trochemical cell, suîtable for secondary use (rechargeable~.
In recent times, increasing atten-tion has been given to the development of energy storage mechanisms.
These developments have, however, been retarded to varying degrees hy the difficulties involved in effectively controlling mobile electrochemically active substances, and by the difficulties involved in operating at the elevated temperatures which in many cases are necessary for the effective operation of electrochemical cells.
~ ccording to one aspect of the invention, khere is provided an electrochemical cell which comprises an anode which includes as its electrochemically active anode material an electronically conductive electropositive substance which is molten at the operating temperature of the cell, a compatible electrolyte; and a compatible cathode, the cell further comprising a substantially non-electronically conductive micromolecular sieve carrier wherein the electro positive substance is sorbed and is held in dispersed form, the micromolecular sieve carrier being liquid-tight and located between and separating the electrolyte and cathode from the electropositive substance of the anode.
By liquid-tight is meant that all of the electro-chemically active species, when going from the anode to the ' 6~
: -3-cathode or vlce versa, has to go via the internal ore (cavity structure of the carrier~.
'..~
, According to another aspect of the invention, there is provided a composite anode structure cornprising a subs~anti.ally non~electronically conductive ~icro-molecular sieve carrier wherein electrochemically active anode :. material in the form of an electronicall~ conductive electro-positive substance is sorbed and held in dispersed form; and a reservoir or source of the electropositive substance in contact with the carrier, for use with a compatible electrolyte and cathode in an electrochemical cell wherein the electropositive substance of the reservoir is molten and is separated by the carrier from the electrolyte.
` Without being bound by theory, the Applicant believes that .~ the electropositive substance may form electronically conductive .~ pathways extending along at least some of the channels and/or pores in the carrier, thereby placing at least so~e of the windows in the surface of the carrier in electronic contact with one another via the interior of the carrier. These path-~ ways, in use, can thus act to render the carrier, when it i5 r doped with the electropositive substance, electronically . conductive as a whole, via the pathways, so that electrons can be conducted along the pathways from the interface between the . carrier and the electrolyte, to the interface between the carrier and the el.ectropositive substance of the anode~
., ' ` ~: ' .
`,........... .
7~
` , --'1--The Applicant believes that it may be possible that the electropositive substance is sorbed in elemental form, the electropositive sub`stance being held in dispersed form in the carrier, and being mobile in atomic or elemental form along the channels and/or pores of the carrier to occupy suitable sites which have beèn vacated by other atoms of the electro-positive substance, so that it can move, in use, through the carrier from -the anode to the electrolyte.
When there is a danger, as when the electrolyte is liquid at the operating temperature of the cell, that the electro-positive substance may react chemically in an undesirable fashion with the electrolyte, e.g. with anions of the electrolyte, the carrier, when it contains the sorbecl electro-positive substance, may be selected or modified such that the windows in its surface to its microporous interior, prevent sufficient access to the interior of the carrier of e.g. the anions of the electrolyte, for the undesirable reaction to take place. Likewise, when as described hereunder the electrolyte selected is an aqueous solution, the carrier, when containing the sorbed electropositive substance, may be selected or modified such that the windows or pores in its surface do not permit access to its interior of water molecules.
The electropositive substance will be molten at the operating temperature of the cell and may comprise or include an alkali metal or alkaline earth metal, a combination or alloy of two or more alkali metals or alkaline earth metals, or a combination or alloy of one or more alkali metals or alkaline earth metals with one or more other substances. In other ~;
7~
words, the alkali metal or alkaline earth metal or metals may be used alone or in combination of -two or more thereof, or one, two or more thereof may be used in a composition or alloy with one or more compatible other substances, provided they are such that the electropositive substance is molten at the operating temperature of the cell.
~ he al~ali metal or metals of the electro-positive substance may be in any suitable combination containing for example lithium, sodium, and/or potassium. The alkaline earth metals may likewise be in any suitable combination of alkaline earth metals, such as calcium or magnesium. The electro-positive substance, as mentioned above, is molten at the operation temperature of the cell. For use at atmospheric pressure, certain alloys of sodium and potassium are particu-larly suitable as they have melting points below 100C, and potassium and particularly sodium can be considered for use alone because of their availability at competitive prices.
.
By 'micromolecular sieve carrier' is meant a molecular sieve carrier having interconnected cavities and/or channels in its interior and windows and/or pores in its surface leading to said cavities and channels, the windows, pores, cavities and/or channels having a size of not more than 50 Angstroms and preferably less than 20 Angstroms, or, when for use with an electrolyte which is an aqueous solution, such that water molecules cannot be sorbed into the interior of the carrier, irrespective of whether other sorbed species are present in the cavities of the carrier.
~ .1767~
Suitable micromolecular sieves are minexal micromolecular sieve carriers, i.e; inorganic lattice or framework structures, although certain essentially organic micromolecular sieve carriers such as clathrates may, in certain circumstances, be suitable as mentioned hereunder.
Suitable mineral micromolecular sieve carriers may be selected from tha group of substances which make up the ; tectosilicates, i.e. the class of substances also known as "framework silicates" which may be natural or synthetic, crystalline or non-crystalline/amorphous, and which include:
silicates, e.g. silica gel zeolites felspars felspathoids being silicates of a structural type in which all four oxygen atoms of the silicate tetrahedra are shared with neighbouring tetrahedra. rrhe framework of the tectosilicate is made up of silicon atoms ~ith in some cases aluminium atoms, together with other atoms. Mineral micromolecular sieves include also mixtures of or analogues of tectosilicates in which the silicon and/or aluminium atoms of the framework may be substituted amongst others by atoms of one or more of:
lron beryllium boron phosphorous carbon germanium and gallium .
,;
~ 17~0~
in minor or major proportions and wherein the micromolecular sieving characteristics and properties are unaffected by the substitution. As long as their properties relevant to the present invention are substantially unaffected, these analogues are regarded as tectosilicates in the context of the present specification.
Conveniently, for molten salt electrolytes, the micro-molecular sieve carrier is a zeolite, or when the electrolyte is to be a~ueous, the carrier may he a tectosilicate which cannot sorb water e.g. a felspar or ~elspathoid.
- Zeolites, felspars and felspathoids are in a class of crystalline or amorphous natural or synthetic materials which contain aluminium and silicon in fairly definite proportions, . .~
and their analoyues. For a more detailed discussion of zeolites, reference can be made to the January 1~75 publication of the International Union of Pure and Applied Chemistry entitled 'Chemical Nomenclature and Formulation of Compositions, of Synthetic and Natural Zeolites'.
Zeolites contain sorbed water molecules which may be removed, usually reversibly, by heat and/or evacuation. While it is e~pected that zeolite molecular sieye carriers which are at least partially dehydrated and usually ~ully dehydrated will generally be used, the presence of water in the zeolite may, in certain cases, be an advantage to enhance ionic conductivity depending on the mechanism of the cell reaction as discussed hereunder.
.
, `
7 ~ ~
Zeolites felspars and felspathoids are usually possessed of a reasonably ord~ered internal structure, exhibit a high internal surface area and are characterised by the presence of a multiplicity of regular arrays of molecular cayities, i.e.
channels and/or cavities opening out of the surface of the ~eolite via windows and/or pores. Other tec-tosilicates, particularly if amorphous or non-crystalline, have a substan-tially less ordered or indeed unordered internal structure, while however retaining suitable arrays of molecular cavities.
It is believed that zeolites i.n their hydrated form can be represented by the following structural formula:
M2~nO-A1203-xsiO2-yH2 where M is a cation of n valance; and X and Y are independent variables that are a function of the composition of the starting mixture, and the manner of formation.
It has been found that suitable tectosilicate crystals can have a sufficiently high physical strength for effective use in the cell of the invention. ~When the tectosilicate is a powder, it may be compacted and supported, for example in a porous container for use).
In addition, it has been found that tectosilicate crystals which have been doped with an electropositive substance can be sufficiently resistant to electrochemical and thermal damage during repeated use in a cell according to the present invention.
~;......
' ' ,,~ ~, 67~
When crystalline tectosilicates are used, physical or electrochemical failure of tectosilicates doped with the electropositive substances should thus not be factors which contribute significantly, if at all, towards failure of cells according to this invention.
In the present invention the micromolecular sieve carrier is de~igned to havè a three-dimensional structural skeleton which remains physically and electrochemically stable, so that it will not collapse significantly as a result of the electro-chemical reaction during normal use, and will continue to function as a sieve permitting diffusion therethrou~h of the electropositive substance, while prevent.ing access to the electropositive substance in its interior by anions of the electrolyte with which it is used, in cases where the anions react undesirably with the electropositive substance of the anode, and preventing access to water when the electrolyte is an aqueous solution.
These aspects should thus be borne in mind in selecting the particular molecular sieve carrier for use with the selected electropositive substances and electrolytes in carrying out the invention.
It should be noted, however, that when certain carriers are doped with extremely electr.opositive substances such as lithium metal alone or in combination with other metals, substantial modification of the carrier lattice can result. It has been found, h~wever, that such modified lattices still ' ' .
~ ~670~
possess the necessary properties in that they can act as carriers andjor sieves for the electropositive substance, are sufficiently electrochemically inert or relati.vely electro-chemically inert during use in a cell, and can preven-t access to the electropositive substance by undesireable chemical species or, when presen-t, water from the electrolyte.
Such carriers, for example tectosilicates such as zeolites which have been physi~ally and/or chemically modified during doping with the selected electropositive substances/ but which still possess the necessary properties, may thus be usefully employed as micromolecular sieve carriers in the anodes o~ this invention, and for the purpose of this specification, these modified tectosilicates, zeolites, etc., are still regarded as tectosilicates, zeolites, etc.
It should further be noted that in the case of some tectosilicates incidental cation exchange may occur during use of the anodes in ac~ordance with the invention, in some electrochemical cells. Such reactions are well known and merely change the sizes of the windows and pores of the carrier lattice, and this aspect should be borne in mind in selecting ~;
:~ the electropositive substance and carrier, to ensure that the ;. pores or windows of the carri~r are of a desired size to permit passage of the electropositive substance therethrough, while excluding water of the electrolyte when an aqueous electrolyte . is used in the cells, and undesireable anions of the electrolyte in cases where these anions are chemically unstable with ;
. ' ,,; ' . ~ :''' ~ '''`-' 7 ~ ~
respect to the electropositive substance. Once again,these are still regarded as -tectosilicates of the type in question.
Thus, it should be appreciated that while the tectosilicate molecular sieve carriers of this invention may, in certain instances, after doping or after having been subjected to several charge/discharge cycles in a cell, no longer strictly be in the form of tectosllicates as such in the usual sense, they may still be regarded as such, or at least as mineral micromolecular sieve carriers in the context of this invention, provided they exhibit the requisite properties.
.
Thus, where the tectosilicate molecular sieve carriers of the eleetrodes of this invention are in the form of modified tectosilieates, they are such that while physieally or ehemically modified, they still possess the appropriate molecular cavities or pores for receiving the electropositive substance, still possess the channels or pores which lead to the cavi~ies, and still have windows of the appropriate size.
Thus, where the moleeular sieve carriers of this invention are in the form of modified substances, they will be those which have windows, channels, pores and cavities for receiving the electropositive substances, and for permitting passage therethrough of the electropositive substances, while excluding water and/or undesireable electrolyte anions.
.
." . ' ', ' , ' . ' .
1 ~76'`~
By taking into consideration factors such as pore or channel size, cavity size and window si~e, and the ability to sorb electropositive substances in effective ~uantities, while permitting high mobility or passage therethrough of the electropositive substances and while excluding water and/or such anions of the electrolyte which are unstable with respect to the electropositive substances therefrom, a rough guide can be obtained for the selection of the appropriate micromolecular sieve carriers for use in accordance with the inven-tion.
Further factors which can serve as a guide, can be the degree of porosity, the density, the availability, and the mechanical strength, the stability and the electronic conductivity or absence thereof, of the doped micromolecular sieve carriers.
.~ .
For example, sodalite has the right structural properties to permit it to function as deseribed herein as a micromolecular sieve carrier for the purpose of this invention. Such alumino-silieates, or the like, which exhibit acceptable structural properties to function as required by this invention, may be suitable tectosilicate molecular sieve carriers~
The micromolecular sieve earrier should preferably thus be such -that the electroposi-tive substance when sorbed therein, will be held therein in finely dispersed elemental form, e.g.
possibly in atomic, mole.cular, atomic cluster or molecular cluster form to present its greatest availability for electrochemical activity during use.
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670~
The carrier should further preferably be such that it will hold an effective amount of the electropositive substance therein for effective electronic, and if necessary ionic, conduction for the electropositive substance to move there-through in effective quantities.
In the present invention, it is believed -that the carriers may in fact act as sieves, permitting dif~usion therethrough of the electropositive substances in elemental, atomic or ionic form from the anode to the electrolyte during discharge of the cell, while preventing access to the electropositive substances contained therein hy water and/or the anions of the electrolyte if unstable with respect to the electropositive substances. In use, the function of the carriers is thus to prevent reduction of the electrolyte by the electropositive substances contained in the anode, and to prevent reaction of these electropositive substances with any water in the electrolyte. It is contem-plated that the cell of the present invention can, if desired, be used as a secondary or rechargeable cell, and during charging, the electropositive substances will diffuse from the electrolyte to the anode.
The anode structures of the present invention are of particular utility in electrochemical cells employing liquid molten salt electrolytes or aqueous solution electrol~tes and designed to operate at relatively low temperatures, for example, of the order of room temperature up to about 360C.
,~
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In such cells, the cathodes can comprise an oxide of one or more transition -m~etals selected for example ~rom the group consisting of ma~ganese, iron and nickel~ or an intermediate refractory hard metal compound of at least one metal selected from the group consisting of chromium, manganese/ iron, cobalt and niakel, with at least one non-metal selected from the group consisting of carbon, boron, nitrogen, silicon and phosphorous which has been activated by halogenation. Thus, for example, the cathode may comprise a refractory hard metal compound which is an activated carbide, of iron~ chromium or manganese.
:'~
Instead, the cathode may comprise sulphur and/or selenium, and a micromoleaular sieve carrier, for example a tectosilicate, '~! wherein the sulphur and/or selenium is sorbed, and is held captive during use of the cathode in the cell. The sulphur and/or selenium may for example be sorbed into a dehydrated ; zeolite molecular sieve carrier which may be selected from the group consisting of erionite, faujasite, synthetic zeolite 3A, zeolite 4A, and zeolite 13X. The zeolite carrier material will be made electron conductive by addition of a suitable electron ` conductive material such as graphite.
: .
:, For such low temperature cells, the electrolyte may be an aqueous acid or base, for example an aqueous solution of sodium hydroxide or potassium hydroxide, or it may be a molten inorganic salt such as an iodide-based inorganic salt electrolyte.
Thus, to test this possibility, the eutectic mixture of lithium iodide/po-tassium iodide was prepared in the ratio described by "
~:, . ~ .. . . .
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~ ~6~0~
; D B Leiser and A J ~hittemore Jr. ~ ~mer. Ceram' _oc. 50 (19611, 60. This mixture was doped with ~9,5~ pure strontium iodide o~tained from Cerac Inc. The components were mixed and qround toget~er into a Eine powder and melted in glass tubes under à flowing stream of argon gas.
~:
The -temperatures were recorded where -the mixtures 1 melted and solidified. The homogeneous solid mixtures were subsequently ground and accurate melting point determinations were carried out. The strontium iodide added varied ~etween about 25~ and a~out 5Q~ ~y mass of the mixture. Melting points were found to lie in the region of 220C and 240C, ,.
whereas the lithium iodide/potassium iodide eutectic mixture was confirmed to melt at about 260C.
,-,;
. ~
Instead the electrolyte may ~e a molten inorganic salt electrolyte ha~ing the general formula:
i M ~l Hal4 in which M comprises one or more alkali or alkaline earth metal cations and Hal comprises one or more halides, the proportions ,~ of the alkali or alkaline earth metal cations and halide anions ' conveniently being such that the above s-toichiometric product , ,':
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1 ~7~70~
is maintained, and the alkali metal cations and halide anions being selected such that the electrolyte has a sufficiently low melting point to permit use in its molten state at the desired operating temperature of the cell.
When such electrolyte is used with a tectosilicate-based :~ carrier, and the electropositive substance of the anode, (for ~ example one or more alkali metals) is capable of reducing the .~; aluminium of the electrolyte to cause :it to plate out on the anode and/or separate from the electrolyte for example to .. precipitate, the window or pore size of the molecular sieve :
carrier of tha anode should be such that the windows exclude the Al Hal41 anions of the electrolyte Erom access to the interior of the zeolite of the anode. When these halide ions are AlC141 , the window or pore size o~ the tectosilicate should be such as comfortably to exclude these anions, whereas easily to permit access via the windows or pores to the interior of the zeolite of the electropositive material, for example atoms or ions of lithium, sodium and/or potassium.
'''''`~'~
. In this way, the Al Hal41 anions are prevented from :- coming inta direct contact with the electropositive material in : its elemental or atomic/molecular form, so that reduction and separation of the aluminium by means of a back reaction cannot ,,,. ,:
directly and easily take placeO
.... .
Tectosilicate molecular sieve carriers which are suitable :
~ for use in conjunction with mol-ten salt electrolites of the , !,. .
;~. formula M Al Hal4, may be selected from the group consisting in :, .' ' ' .
?.~r.. ~ : , .~,, .
..... .
,: ' `; ~ 1176700 ~ . ~
sodalitel carnegieite, zeolite 4A, zeolite 13X and mordenite.
In the case of aqueous electrolytes, testing them as the electrolytes in cells according to the invention having sodium/potassium anodes and cathodes comprisin~ manganese dioxide promises to provide excellent electrochemical ~ehaviour at operating temperatures below 100C.
, When such electrolytes are used with a tectosilicate-~ased carrier, the electropositive su~stance of the anode, (for example one or more alkali metals~ is capable of reacting with the water of the electrolyte, so the window or pore size of the molecular sieve carrier should be such that the windows exclude the water of the electrolyte from access to the interior of the anode. The windo~ or pore size of the tectosilicate should be such as comfortably to exclude water, whereas easily to permit access via the windows or pores to the interior of the anode of the electropositive material, for example atoms or ions of sodium, lithium, and/or potassium.
In this way, ~ater is prevented from coming into direct contact with the electropositive material in its elemental or atomic/molecular form, so that the undesired reaction cannot take place.
,, :.
: ,.;;, 1~ " ., ~ ~ithout being bound hy theory, it is ~elieved that in micromolecular sieve carriers which have cavities in the form ,.: .
i of capillary- or pipe-like channels, which may have a , ~
.
. .
, . ~
7~
approximately e~ual to the pore or windo~ ~ize, the electro-positive substan:ce can possibl~ move alony th.e channels during discharge from th.e source o~ electropositive material ~ to the in-terface ~etween the carrXer and the electrolyte, ;l and that in certain instances the electroposi-tive suhstance in the channels may maintain electronic contact with the . elec-troposi.tive substance reservoir throughout the body of the carrier. In oth.er words, the carrier will, in this ~ case, be electronically conductive, via the electropositive :: substance in the channels, between th.e reservoir or source of electroposi.tive substance and the electrolyte. In this : regard it will be appreciated that the source of electropositive : .
^- substance will not ~e in direct contact with the electrolyte, except via the doped micromolecular sieve carrier.
.
:i.$`
. ~ In the case where the doped molecular sieve carrier is an electron conductor, one possible mechanism is that during :~ ~ discharge of the cell, atoms of the electropositive substance ~ ionize at the interface between the electrolyte and the }-,;'`.~
molecular sieve carrier, and the ions pass into the electrolyte, .. the eleotrons from said ionizat.ion passing via the electro-j~ positive su~stance in the interior of the carrier to said : source of electropositive material, which will act as or can be ,: ~ .....
associated with a current collector. At the same time, atoms of the electropositive substance will pass from said source of anode material into the molecular sieve carrier material to replace those which have been ionized, rapid diffusion of the :, ~ ., .
.. ,~
,' :
-~''';
.' ' .
, .
1 ~7~0~
electroposi-t~ive material taking place via the channels of the molecular sieve carrier from the anode towards the electrolyte.
According to this mechanism, the electropositive substance may be present in the form of electronically conductive threads or chains in the channels. It is possible, however~ that, instead of the electropositive substance being present in the Eorm of electronically conductive chains or threads in the channels, the elec~rochemically active sorbed electronically conductive substance atoms may form clusters with suitable cations forming part of the lattice or matrix o~ the molecular sieve material. These clusters may thus share electrons from the sorbed electropositive substance. Such electrons may be sufficiently mobile to move through the molecular sieve carrier from its interface with the electrolyte where ionization takes place, to the anode reservoir and thence to the collector.
... .
If the mechanism suggested above whereby ionization takes place at the interface between the molecular sieve carrier and . ~
the electrolyte is, however, incorrect and ionization takes place at the interface of the molecular sieve carrier and the anode or source of electro-positive substance, or a hybrid mechanism exists whereby ionization at the source is sufficient-ly predominant, then the molecular sieve carrier with the electropositive substance sorbed therein may not, strictly speaking, function as a sieve, but may instead function as a solid electrolyte. Ions instead of atoms will then diffuse rapidly through the molecular sieve carrier. This process may be enhanced by the presence of sorbed atoms in the form of 67~ ~
clusters, the solid electrolyte being metal rich, e.g. Na43+
clusters in sodali~e. However, whe-ther or not the carrier impregnated with the electropositive substance is regarded as a sieve or solid electrolyte, this does not affect its utility and function as described above, in the cells and anode structures of the present invention.
:
To prepare a carrie~ according to the invention~ a tectosilicate, for example a suitable felspar or felspathoid or .- .
~ a zeolite w~ich is fully or partially dehydrated by subjecting ,.~
it to vacuum and heat, is exposed, optionally under pressure and after having been subjected to a vacuum, -to a vapour of the electropositive substance to be sorbed into it. While it may ,~ not be necessary to saturate all the vacant sites in the ~ zeolite molecular sieve carrier with the electropositive ~....;
1 ; substance, and only a desired proportion o~ the vacant sites l` ' need be o~cupied thereby, in practice it is contemplated that as much of the electropositive material as possible will be sorbed into the zeolite molecular sieve carrier.
Pore or window size of the zeolite molecular sieve carrier may or may not, as the case may be, be modified by the sorption of the electropositive material, and the zeolite molecular sieve carrier will be chosen 50 that its channel and pore sizes, in particular its window sizes are, after doping, such ,,i, ; tha-t it operates effectively to exclude any anion which is unstable with respec~ to the alkali metal of the anode, or any ~ water from the electrolyte from reacting with the electro-:, ..
.:
:`:
`: : ` :
7~
positive substance in the channels in use. In other words i~
such modification takes place, the micro molecular sieve carrier and metals may be chosen so tha-t the molecular sieve carrier finally obtained has suitable channel, pore and window sizes.
Thus, lithium, sodium or potassium may be used alone or such alkali metals may be used together, or they may be used together with other metals such as, for example, aluminium. It is believed that when an electropositive substance such as sodium or lithium is used together with another metal such as aluminium, both the alkali metal and the other metal such as aluminium, may be sorbed in the carrier, the other metal modifying the zeolite molecular sieve carrier by reducing effective channel, pore and/or window sizes to a desired value appropriate for the intended use of the anode. Thus, starting with a molecular sieve carrier which has channels, pores and particularly windows which are too large to exclude undesire-able electrolyte ions, after sorption of the other metal these channels, pores and/or windows may be reduced in size by the presence of atoms of the other metal occluding them, so that they are at the right size to exclude any water or undesireable electrolyte ions, while permitting passage or entry of the electropositive alkali metal atoms/ions such as sodium, potassium and/or lithium.
.
The possibility is also contemplated that when the pore size of the carrier is sufficiently large, molecules of the electrolyte may, in the initial stage o~ the operation of the cell, be able to penetrate some way into the body of the carrier, .
' ' `' 7 0 ~
at which point a reaction will occur with the electropositive substance, the res~ultant products of which serve to reduce the cavity size, thereby preventing further penetration of the electrolyte and any further reaction, so that the action of the cell is as described above, e.g. when sodium is the electro-positive material, sodium aluminium chloride i5 -the li~uid electrolyte, and the reaction causes precipitation of aluminium metal which serves to block the cavities to the desired extent.
, .: It will thus be appreciated that ~ither a suitable molecular sieve carrier can be selected which initially has .... .
windows, pores and channels of the correct size, or one having ~ such sizes which are too large, can be selected and modified .s during the sorption process so that lt ends up with the pores, . channels and windows of the appropriate size. In this case, ~ . -s ::' the other metal, such as aluminium, or even nickel, which is .~ used together with the electrochemically active electropositive :;~
alkali metal, can form an effective lining to the channels, to remain there while being relatively electrochemically inert in the cell, acting to reduce the channel, pore and/or window sizes, and acting also to increase electronic conductivity along the pathways provided by the channels containing the electro-chemically active electropositive substance. Thus, certain species of the sorbed material can act to modify the molecular sieve carrier and to stabilize it while increasing its electronic conductivity along the pathways provided by the channels, whereas other species can act as -the electroposi-tive material. The electron-conducting properties of the molecular sieve carrier can thus, it is believed, be confined to the 7 ~ ~
channels, whereas the body of the molecular sieye carrier material or at least that part thereof which is in direct contact with the liquid electrolyte, will be non~, or neylig.i~
bly, electronicall~ conductive to prevent plating of cations from the electrol~te onto the surface of the anode exposed to the electrolyte during charging.
This feature acts to prevent dendrite formation which is in many instances a cause of cell failure, since the plating of the electropositive material can only take place inside the cavity structure of the carrier, thereby preventing it from becoming detached from the anode structure and/or causing internal short circuits.
;~
In specific embodiments of the invention when the carrier ' ~ is a zeolite, the anode can comprise sodalite with sodium sorbed therein; mordenite with suitable proportions of potassium and sodium sorbed therein; or mordenite with ~ .
suitable pr.oportions of potassium and lithium sorbed therein.
In a further specific embodiment of the invention, where the material of the molecular sieve carrier is a non-, or negligibl~, electronically conductive zeolite, it may be possible to dispense with a separate liquid electroly-te and to have the zeolite molecular sieve carrier in direct and in-timate contact with a suitable compatible cathode, such as sulphur sorbed into graphite-coated zeolite 4A. In this case, the :
sulphur (in the form of polysulphide) can act as the electrolyte and the zeolite with sulphur sorbed therein can be regarded as , . . .
~ 4-a catholyte. In this instance, thus, the zeolite/sulphur catholyte is regarded as a combined electrolyte/cathode and the , ., cells of the invention contemplate this possibility, with references to electrolyte and cathode in the context to be ~ construed accordingly. If the zeolite material of the anode is ;~ too electronically conductive to permit this, it may, however, . . ~, } be necessary to provide a porous insulating layer between the carrier and the cathode, impregnated with a suitable liquid electrolyte. This porous insulating layer may be a suitable insulating undoped dehydrated zeolite material. This embodi-;~ ment has the advantage that, apart from the anode or source of ,~i::
electropositive material, which will generally be molten, the cell will be substantially solid and zeolite-based.
, ,~ .
.;
It is further contemplated, when the cell can operate at a sufficiently low temperature, clathrate micromolecular - sieve carriers can be used in the same way as the previously , ., . mentioned mineral micromolecular sieve carriers. They should - not, when used with aqueous electrolytes, for the same reasons, ~: .
~- be capable of sorbing water, and should have a similar channel-` type structure, and similarly non-tectosilicate oxide micro-` molecular sieve carriers may be used.
The invention will now be described, by way of example, with reference to the accompanying diagrammatic drawings, in which Figure 1 shows a schematic diagram of a device used as a conductivity cell for conductivity tests carried out on a zeolite carrier for a cell according to the invention;
. '' .
' ,. : , .
o ~ ~
Figure 2 shows a similar diagram o~ a test cell according to the invention; and Figures 3 and 4 show graphical results of tests conducted with the device of Figure 1.
. ' ~
In Figures 1 and 2 of the drawings, the same ; reference numerals are used for the same parts, unless ,~
otherwise specified.
In Figure 1, a conductivity cell generally designated 10, comprises a pair of stainless steel cups 12 held together by peripherally spaced insulated locking screws 14. In the cups 12 are molten alkali metal electrodes 16, and they are separated by a carrier 18 for a cell according -to the invention.
The carrier is clamped between the rims 12.1 of the cups 12 and acts to separate the electrodes 16 from one another.
In Figure 2, essentially the same arrangement is shown, except that one of the electrodes 16 is replaced by a liquid electrolyte/cathode mixture 20, so that the electrode 16 iS an anode and the cups 12 act as current collectors.
'''.
The invention will further be described, with reference to the following non-limiting examples, carried out with the device and the cell of Figures 1 and 2.
:;' ~) . :
:
. ~
; EXAMPLE 1 With reference to Figure 1, the carrier 18 was made in the form of a compact or pellet containing zeolite 4A and kaolin. A
mixture of equal parts by mass of zeolite 4A and kaolin was ball~milled for 24 hours, and a pellet was pressed on a linear ;~ press at a pressure of 2x105 kPa. The pellet was fired at 650C for 3 hours. After cooling, the artifact was placed in a ~` ~ freshly prepared zeolite 4A gel in which the kaolin was converted to zeolite 4A and the pel:Let was further densified by ~ 1 .'" .
~c~ back impregnation of the zeolite 4A from the fresh gel.
' ~' `
- The fully densified pellet artifact was removed from the ge:L
,~1~,~
i after 10 days, washed with distilled water and dehydrated at ``;~ 360C and 10 kPa for 6 hours. The pellet was then subjected to : sodium me-tal impregnation from the gas phase under a vacuum at 350C for 2-3 hours.
! .:
The pellet loaded with sodium sorbed therein was then handled ~ in a glovebox containing dry argon, and the device of Figure 1 `~I was constructed, and electrically connected to form a conduc-tivity cell. This procedure was repeated a number of times, and a number of such conductivity cells were constructed, employing also potassium and lithium as dopants.
Alternatlng current (AC) resistance R, against temperature T, was measured for the pellets. A typical graph of pellet conductivity as log 0' T (wherein ~ is the specific conductivity defined as = A R where d is pellet thickness, A is pellet ':
: .
~ .
'~`"' '' :
:
, .~
~ 67 û ~
:~ -27-cross-sectio~nal area, and R is the measured resistance in ohms) against temperature ( T 1 is shown in Figure 3.
. .
Comparative summarised test results are set out in the - following Table, Table 1 which compares a sodium impregnated :~ pellet with pellets impregnated with lithium and potassium respectively:
; TABLE 1 , Metal (5~cm) 1 TC
. Li 0,006 350 . Na 0,050 350 ~: K 0,010 350 :
Further compacts or pellets were made containing zeolite 4A.
..''`' The pellets of Example 2 were then dehydrated and treated with sodium, as described in Example 1 and tested at different temperatures.
.
~ Figure 4 shows a typical plot of log~T against 10 using the conductivity cell of Figure 1.
Test resul-ts are summarized in -the following Table, Table 2, ror sodlum:
'~:
~,',,., ` "
~, '` ` (-Lcm) 1 TC
~`:"; 0,006 20Q
0,020 250 ~.
~`. 0,060 300 ., .
~ ..
~^;. EXAMPLE 3 ~.
Small electrochemical test cells were made in accordance with Figure 2, comprising an alkali metal anode 16, a zeolite having the alkali metal sorbed therein as the pellet 18, and a suitable compatible liquid electrolyte and cathode 20. A test was conducted using a sodium anode, a zeolite 4A impregnated with sodium as the pellet, and a potassium iodide/ lithium iodide molten salt electrolyte mixed with cathode materi.al comprising zeolite 13X crystals doped with sorbed sulphur and containing graphite for electronic conductivity. In this case, an open cuxrent voltage of 1,9V was obtained together with a short circuit current of 35 mA, with an effective surface area of about 1 cm2 at 300C.
A further cell was constructed using potassium for the anode, a zeolite 4A for a pellet impregnated with potassium, a lithium aluminium chloride electrolyte and a zeolite 4A containing impregnated sulphur as the cathode.
In this case, an open current voltage of 2,0V was obtained, with a short circuit current of 5 mA at a temperature of 200C, with an effective surface area of about 1 cm2.
; ,"1 '`'' '','.
~' ' ~ ,,.
. . .
-29~ 70~
. -:; Finally, a cell was constructed using a sodium anode, sodium ; impregnated into a zeoli-te carrier, a sodium aluminium chloride -~ electrolyte, and as a cathode sulphur sorbed into zeolite 4~.
From this cell an open current voltage of 1,9V was obtained, with a short circuit current of about 10 mA, at 200C with an :~ effective surface area of about 1 cm2.
. ~ .
.~, In all the above cells, the zeolite of the carrier was prepared by mixing with kaolin as described in Example 1.
' .1 .
~, .
All the cells described above failed at various times, for reasons essentially unrelated to the electrochemistry thereof, such as sealing problems, artifact cracking, etc. I-t is expec-ted that routine experimentation will overcome these problems. While some of these cells failed after a matter of .:
~ `, hours, others lasted up to 7 days.
: ~ ;
` An advantage of the present inven~ion is that it provides a cell in which the electrolyte is separated from the anode by a carrier which has a conductivity several orders of magnitude I higher than that of undoped tectosilicates, e.g. the zeolites reported in Breck, Donald W. 'Zeolite ~olecular Sieves', published by John Wiley & Sons, 1974, at pages 397 to 410.
, ~
It should be noted that the carrier tested, as appears ~rom Figures 3 and 4 hereof, has a conductivity which increases with the operating temperature i.e. it shows a positive temperature coefficient of conductivity which indicates that the conductivity may be ionic or hybrid rather than purely metallic or electronic.
..
' 7 ~ ~
. .
..
As regards the construction of the carrier of the present invention, it is intended to be completely liquid-tight in use.
For this reason ever~ attempt should be made to make it completely dense, with no macroporous spaces, channels, etc., therein. As regards its function, it should further be noted that, after such initial stabilization or conditioning period as may be necessary, there is in fact no change in the average chemical composition of the carrier during charging and :
discharging, and no change in the average oxidation state of the electropositive substance therein.
,'`, :.
Claims (17)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. An electrochemical cell which comprises an anode which includes as its electrochemical active anode material an electronically conductive electropositive substance which is molten at the operating temperature of the cell;
a compatible electrolyte; and a compatible cathode, the cell further comprising a substantially non-electronically conductive micromolecular sieve carrier wherein the electro-positive substance is sorbed and is held in dispersed form, the micromolecular sieve carrier being liquid-tight and located between and separating the electrolyte and cathode from the electropositive substance of the anode.
a compatible electrolyte; and a compatible cathode, the cell further comprising a substantially non-electronically conductive micromolecular sieve carrier wherein the electro-positive substance is sorbed and is held in dispersed form, the micromolecular sieve carrier being liquid-tight and located between and separating the electrolyte and cathode from the electropositive substance of the anode.
2. A cell as claimed in Claim 1, in which the electrolyte is liquid at the operating temperature of the cell and can react undesirably with the sorbed electropositive substance, and in which the carrier is selected or modified so that the windows in its surface to its microporous interior prevent sufficient access to its interior for such undesirable reaction to take place.
3. A cell as claimed in Claim 1, in which the electropositive material of the anode is selected from the group consisting in alkali metals, alkaline earth metals, combinations or alloys of two or more alkali metals and/or alkaline earth metals, and combinations or alloys of one or more alkali metals and/or alkaline earth metals with one or more other substances.
4. A cell as claimed in Claim 3, in which the electro-positive substance is sodium or an alloy of sodium and potassium.
5. A cell as claimed in Claim 1, in which the carrier is a mineral micromolecular sieve carrier.
6. A cell as claimed in Claim 5, in which the carrier is a tectosilicate.
7. A cell as claimed in Claim 6, in which the tectosilicate is selected from the group consisting in zeolites, felspars, felspathoids and silicates.
8. A cell as claimed in Claim 7, in which the electrolyte is a molten salt electrolyte, and the carrier is a zeolite.
9. A cell as claimed in Claim 7, in which the electrolyte is aqueous inorganic salt solution, and in which the carrier is a felspar or felspathoid.
10. A cell as claimed in Claim 1, in which the cathode comprises as electrochemically active cathode material a substance selected from the group consisting in oxides of one or more transition metals, activated intermediate refractory hard metal compounds, and sulphur or silenium sorbed in a micromolecular sieve carrier.
11. A cell as claimed in Claim 1, in which the electrolyte is selected from the group consisting in aqueous solutions of bases, acids, and inorganic salts, and molten inorganic salts.
12. A composite anode structure comprising a substantially non-electronically conductive micro-molecular sieve carrier wherein electrochemically active anode material in the form of an electronically conductive electro-positive substance is sorbed and held in dispersed form; and a reservoir or source of the electropositive substance in contact with the carrier, for use with a compatible electrolyte and cathode in an electrochemical cell wherein the electropositive substance of the reservoir is molten and is separated by the carrier from the electrolyte.
13. An anode structure as claimed in Claim 12, in which the electropositive anode substance is selected from the group consisting in alkali metals, alkaline earth metals, combinations or alloys of two or more alkali metals and/or alkaline earth metals, and combinations or alloys of one or more alkali metals and/or alkaline earth metals with one or more other substances.
14. An anode structure as claimed in Claim 13, in which the electropositive substance is sodium or an alloy of sodium and potassium.
15. An anode structure as claimed in Claim 12, in which the carrier is a mineral micromolecular sieve carrier.
16. An anode structure as claimed in Claim 15, in which the carrier is a tectosilicate.
17. An anode structure as claimed in Claim 16, in which the tectosilicate is selected from the group consisting in zeolites, felspars, felspathoids and silicates.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| ZA806256 | 1980-10-09 | ||
| ZA80/6256 | 1980-10-09 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1176700A true CA1176700A (en) | 1984-10-23 |
Family
ID=25574974
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000387044A Expired CA1176700A (en) | 1980-10-09 | 1981-09-30 | Electrochemical cell and an anode structure for an electrochemical cell |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4457989A (en) |
| JP (1) | JPS5795086A (en) |
| AU (1) | AU542196B2 (en) |
| BR (1) | BR8106524A (en) |
| CA (1) | CA1176700A (en) |
| DE (1) | DE3140181A1 (en) |
| FR (1) | FR2492173A1 (en) |
| GB (1) | GB2085220B (en) |
| IT (1) | IT1195279B (en) |
| SE (1) | SE448797B (en) |
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|---|---|---|---|---|
| GB8423961D0 (en) * | 1984-09-21 | 1984-10-31 | Lilliwyte Sa | Electrochemical cells |
| US5728489A (en) * | 1996-12-12 | 1998-03-17 | Valence Technology, Inc. | Polymer electrolytes containing lithiated zeolite |
| US5882624A (en) * | 1997-01-29 | 1999-03-16 | Englehard Corporation | ETS-14 crystalline titanium silicate molecular sieves, manufacture and use thereof |
| DE102010026613A1 (en) * | 2010-07-09 | 2012-01-12 | MAX-PLANCK-Gesellschaft zur Förderung der Wissenschaften e.V. | New phosphate- and silicate-based electrode materials, in particular for lithium-ion batteries and lithium capacitors |
| EP2904659A1 (en) * | 2012-10-05 | 2015-08-12 | Massachusetts Institute of Technology | Low-temperature liquid metal batteries for grid-scaled storage |
| JP6286438B2 (en) | 2012-10-16 | 2018-02-28 | アンブリ・インコーポレイテッド | Electrochemical energy storage device and housing |
| US11721841B2 (en) | 2012-10-18 | 2023-08-08 | Ambri Inc. | Electrochemical energy storage devices |
| US11211641B2 (en) | 2012-10-18 | 2021-12-28 | Ambri Inc. | Electrochemical energy storage devices |
| US11387497B2 (en) | 2012-10-18 | 2022-07-12 | Ambri Inc. | Electrochemical energy storage devices |
| US10541451B2 (en) | 2012-10-18 | 2020-01-21 | Ambri Inc. | Electrochemical energy storage devices |
| US9735450B2 (en) | 2012-10-18 | 2017-08-15 | Ambri Inc. | Electrochemical energy storage devices |
| US9312522B2 (en) | 2012-10-18 | 2016-04-12 | Ambri Inc. | Electrochemical energy storage devices |
| WO2015058010A1 (en) | 2013-10-16 | 2015-04-23 | Ambri Inc. | Seals for high temperature reactive material devices |
| US9520618B2 (en) | 2013-02-12 | 2016-12-13 | Ambri Inc. | Electrochemical energy storage devices |
| US10270139B1 (en) | 2013-03-14 | 2019-04-23 | Ambri Inc. | Systems and methods for recycling electrochemical energy storage devices |
| US9502737B2 (en) | 2013-05-23 | 2016-11-22 | Ambri Inc. | Voltage-enhanced energy storage devices |
| US10181800B1 (en) | 2015-03-02 | 2019-01-15 | Ambri Inc. | Power conversion systems for energy storage devices |
| WO2016141354A2 (en) | 2015-03-05 | 2016-09-09 | Ambri Inc. | Ceramic materials and seals for high temperature reactive material devices |
| US9893385B1 (en) | 2015-04-23 | 2018-02-13 | Ambri Inc. | Battery management systems for energy storage devices |
| US10069141B2 (en) | 2015-12-30 | 2018-09-04 | Toyota Motor Engineering & Manufacturing North America, Inc. | Hybrid sulfur particles and cathode active materials containing the hybrid particles |
| US11929466B2 (en) | 2016-09-07 | 2024-03-12 | Ambri Inc. | Electrochemical energy storage devices |
| WO2018187777A1 (en) | 2017-04-07 | 2018-10-11 | Ambri Inc. | Molten salt battery with solid metal cathode |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3736186A (en) * | 1971-06-16 | 1973-05-29 | Mallory & Co Inc P R | Separator and electrolyte material for solid electrolyte battery systems |
| US3891460A (en) * | 1973-05-14 | 1975-06-24 | Catalyst Research Corp | Thermal battery and molten metal anode therefore |
| US3864168A (en) * | 1974-03-22 | 1975-02-04 | Yardney International Corp | Electrolytic cells incorporating water scavengers |
| US4002807A (en) * | 1975-09-30 | 1977-01-11 | Ford Motor Company | Alkali metal, sulfur battery or cell with single phase sulfur electrode |
| CA1093150A (en) * | 1977-03-09 | 1981-01-06 | Johan Coetzer | Cathode, the formation of a cathode, and a cell incorporating such a cathode |
| ZA771433B (en) * | 1977-03-09 | 1978-10-25 | South African Inventions | Cathode and cell incorporating such a cathode |
| CA1123901A (en) * | 1978-07-17 | 1982-05-18 | Johan Coetzer | Electrochemical cell having electrode with zeolite molecular sieve |
| ZA785067B (en) * | 1978-09-06 | 1980-04-30 | South African Inventions | Electrochemical cell |
-
1981
- 1981-09-28 US US06/306,904 patent/US4457989A/en not_active Expired - Fee Related
- 1981-09-29 AU AU75776/81A patent/AU542196B2/en not_active Ceased
- 1981-09-30 CA CA000387044A patent/CA1176700A/en not_active Expired
- 1981-10-08 JP JP56160851A patent/JPS5795086A/en active Pending
- 1981-10-08 GB GB8130474A patent/GB2085220B/en not_active Expired
- 1981-10-08 BR BR8106524A patent/BR8106524A/en unknown
- 1981-10-08 SE SE8105964A patent/SE448797B/en not_active IP Right Cessation
- 1981-10-09 DE DE19813140181 patent/DE3140181A1/en not_active Ceased
- 1981-10-09 IT IT24434/81A patent/IT1195279B/en active
- 1981-10-09 FR FR8119098A patent/FR2492173A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB2085220B (en) | 1984-02-08 |
| FR2492173B1 (en) | 1985-01-11 |
| BR8106524A (en) | 1982-06-29 |
| DE3140181A1 (en) | 1982-05-19 |
| US4457989A (en) | 1984-07-03 |
| AU542196B2 (en) | 1985-02-14 |
| JPS5795086A (en) | 1982-06-12 |
| AU7577681A (en) | 1982-04-22 |
| FR2492173A1 (en) | 1982-04-16 |
| IT1195279B (en) | 1988-10-12 |
| SE8105964L (en) | 1982-04-10 |
| GB2085220A (en) | 1982-04-21 |
| IT8124434A0 (en) | 1981-10-09 |
| SE448797B (en) | 1987-03-16 |
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